Does iOS prefer 3G to wi-fi?

A number of iOS 6 users have filed complaints after seeing a significant swell in their mobile bills, due to a sudden increase in mobile data usage.

There is speculation, The Guardian reports, that it's all down a bug in how iOS 6 switches between 3G and wi-fi connections, pushing users far beyond their data limits.

It could be an error with iTunes Match, which enables users download to copies of their music to the phone from the cloud, or another iCloud synchronisation service.